Field of the Invention
This invention relates, in general, to blood perfusion systems, and more particularly, to an apparatus and a method for rapidly cooling or heating the body temperature of a patient.
Description of the Related Art
Patients who experience severe medical trauma, such as a stroke, heart attack, or cardiac arrest, can benefit from cooling the body to below normal body temperature shortly after experiencing the trauma. Studies have shown that the medical outcome for such patients is significantly improved if they are treated within 90 minutes of arriving to the hospital. During surgery, the patient's body is typically cooled to induce hypothermia in order to protect the organs. In certain medical situations, such as post-surgery, it is desirable to reheat the patient's blood to a normal body temperature. The measure of damage to the cardiac muscle in patients who have had an acute myocardial infarction is directly correlative to the infarcted area. Studies have shown that rapid increases or decreases of the patient's body temperature reduce the infarct size and improve recovery outcome. Similar results have been shown in stroke patients for preserving neurological function and contrast-injected patients to preserve kidney function.
Existing systems and methods for reducing the temperature of a patient include infusion of cold saline through endovascular cooling catheters having separate lumens for saline flow and blood flow. Other systems and methods rely on heating or cooling pads which are applied directly to the patient's body. Cardiopulmonary bypass is a typical method of cooling the patient's heart, while several similar bypass methods are known to cool the patient's brain. These existing systems and methods are often cumbersome and do not reduce the temperature of the patient's body quickly enough to have a beneficial medical outcome. Additionally, existing systems are often only capable of either heating or cooling the patient's body, therefore requiring multiple devices present within an operating room.
Known systems based on extracorporeal blood extraction circuits typically have conduits carrying blood from the patient through heat exchangers in order to perform controlled heating or cooling of the blood. Conduits typically include endovascular catheters inserted into the patient's vascular system. Heat exchangers for cooling the patient's body often include an ice bath for cooling the endovascular catheter directly or cooling the water or saline solution that is passed through a conduit in the catheter. Similarly, heat exchangers for heating the patient's body typically include one or more heating devices for heating the endovascular catheter directly or heating the water or saline solution that is passed through the catheter lumen. In certain devices, a controller may be coupled to a plurality of sensors to regulate the heat exchanger and/or the pump.
Within the prior art, U.S. Pat. No. 7,473,395 to Zviman et al. teaches a hypothermia induction device for recirculating blood through an extracorporeal circuit using a single venous access. The device includes a withdrawal pump, an infusion pump, a chiller and heat exchanger, and optional modules for further blood treatment. A controller adjusts the operation of withdrawal and infusion pumps based on pressures sensed in catheter lines between the patient and the device. This system is only capable of cooling the blood by maximizing the withdrawal rate to maintain a predetermined temperature.
U.S. Pat. No. 7,588,549 to Eccleston is directed to a thermoelectric temperature control device for an extracorporeal blood circuit. The device includes a heat exchanger cassette having a central core and two flow guides in thermal contact with a thermoelectric module. A plurality of parallel channels pass through the cassette to guide blood to and from the device in a substantially laminar flow. A controller regulates the voltage and current of the thermoelectric module to control the temperature differential produced by the device.
United States Patent Application Publication No. 2006/0293732 to Collins et al. discloses a thermoelectric cooler and heat exchanger for an intravascular heat exchange catheter. The system incorporates a secondary heat exchange element in thermal contact with a thermoelectric cooler assembly. Heat is removed from the thermoelectric cooler assembly via a reservoir connected to a circulating fluid supply. A controller regulates the power level supplied to the thermoelectric cooler assembly. Optionally, the controller may also regulate the fluid flow to and from the reservoir.
Numerous disadvantages are associated with the existing devices for heating or cooling the body temperature of a patient. In most known systems, the heater and/or cooler is contained within a separate unit from the pump. This arrangement is bulky in size and therefore requires additional space within the operating room. Additionally, most known systems are capable of either heating or cooling the blood, which requires hospitals to get separate units for both heating and cooling. This duplication not only adds additional expense, but also further reduces the available space in already cramped operating rooms. Furthermore, large pump priming volume is required due to the separation of the pump from the heat exchange element. Many known systems are inefficient at adding heat to and/or removing heat from the patient's blood and therefore require large heat exchangers having a large volume of blood present within them.